Fix graph creation in tck

Summary:
Parsing query with string values wasn't correct. It didn't matter
with which type of quote mark string value started. It simply took
any possible quote mark which wasn't escaped as possible beginning
or end for string value.

Following example didn't work:
{name: "Chris Anderson: Technology's long tail"}

Detected string value was "Chris Anderson: Technology' and because
of that query broke. Now, string is detected by memorizing which
quote mark was used to start parsing string value and is required
to end string value with that quote mark.

Reviewers: teon.banek, msantl

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1029

tests/qa/tck_engine/steps/graph.py

@@ -41,26 +41,26 @@ def create_graph(name, context):
 
     with open(path, 'r') as f:
         content = f.read().replace('\n', ' ')
-        q = ''
-        in_string = False
+        single_query = ''
+        quote = None
         i = 0
         while i < len(content):
             ch = content[i]
             if ch == '\\' and i != len(content) - 1 and content[i + 1] in q_marks:
-                q += ch + content[i + 1]
+                single_query += ch + content[i + 1]
                 i += 2
             else:
-                q += ch
-                if in_string and ch in q_marks:
-                    in_string = False
-                elif ch in q_marks:
-                    in_string = True
-                if ch == ';' and not in_string:
-                    database.query(q, context)
-                    q = ''
+                single_query += ch
+                if quote == ch:
+                    quote = None
+                elif ch in q_marks and quote is None:
+                    quote = ch
+                if ch == ';' and quote is None:
+                    database.query(single_query, context)
+                    single_query = ''
                 i += 1
-        if q.strip() != '':
-            database.query(q, context)
+        if single_query.strip() != '':
+            database.query(single_query, context)
     context.graph_properties.set_beginning_parameters()